This invention relates to apparatus for obtaining certain characteristics of an article and refers particularly, though not exclusively, to apparatus for determining the identifying characteristics of a coin.
Throughout this specification, reference to a coin is to be taken as including a reference to a token.
In our earlier international applications PCT/AU91/00295 and PCT/AU94/00777 there are disclosed methods and apparatus for the discrimination of coins. These apparatus, like the apparatus of the prior art to which they refer, and the remainder of the prior art, use xe2x80x9cpot-corexe2x80x9d ferrites in which electrical windings are inserted. The use of such ferrites results in a complex magnetic field across the face of each ferrite. This is because the coils are in series electrically but are not connected magnetically. When a coin is inserted into the machine in which the apparatus is located, the coin rolls down, or falls, into the gap between the two ferrites. When a coin is in the gap, a complex magnetic field pattern is created. This results in changes in the eddy current losses being induced in the coin, and changes in the inductance of the magnetic circuit. The applications of a dc pulse as described in our earlier international application referred to above results in a specific coin signature which is able to be used to discriminate between coins of various dimensions, metals, and permeabilities. In this way, it is possible to discriminate between coins of different values.
It has been found that factors such as coin speed and, more particularly, the position of the coin within the air gap between the ferrites in such constructions is unpredictable. Furthermore, the dimensions of the air gap cannot be controlled with precision as the two ferrites are mounted on separate components as part of the construction of the apparatus. This may cause a variation in the width of the air gap due to manufacturing tolerances. Also, over time there may be movement of the ferrites to thus alter the width of the air gap. As a result, the coin signatures produced may have a large range of results for coins of the same value. In consequence, it is, at times, difficult to satisfactorily discriminate between certain coins.
Furthermore, the design of the sensor effects the extent of the induced eddy currents produced in a particular coin due to the way in which the coin interacts with the magnetic field imposed upon the coin.
It is therefore the principal object of the present invention to provide apparatus for obtaining certain characteristics of an article where a return magnetic path is provided. A further object is to provide apparatus for obtaining certain characteristics of an article where an air gap of relatively constant width is provided.
With the above and other objects in mind, the present invention provides apparatus for obtaining certain characteristics of an article, the apparatus including an electromagnet inductor with a first end and a second end, the first end facing the second end with an air gap therebetween, there being at least one arm joining the first end and the second end and having electrical windings to generate magnetic flux in the air gap, the arm being a fixed return path for the magnetic flux; the first end and the second end each having a surface area substantially the same as or greater than the surface area of the article.
The windings may be mounted within the arm, or around the arm.
Preferably, the arm is C shaped with the gap being the air gap. Alternatively, the arm may be one arm of a number of arms which, in combination with the air gap, form a rectangle.
The arm may be rectangular, or be of any other shape such as, for example, circular, pear shaped, elliptical or tear shaped.
The ends may have end pieces of greater surface area than the surface area of the ends. The end pieces may be integral with the ends, or may be separate components securely attached to the ends. Preferably, the end pieces are round and are larger in diameter than the largest article to be processed.